Got rejected by my girlfriend for a threesome and I'm going to end our relationship

So I never thought I would write this. I'm in my early 30s and we've been dating for a year and a half. We've been living together for a few months now. Everything was great. I have no complaints. She was the first girl I really loved.<br><br>I don't know if it's my ego, or my complicated past that's bothering me. I'm a victim of sexual assault. So I've always been insecure about it. She knew about all of this and has always reassured me about it. <br><br>A few months ago, I opened up to the idea of a polygamous relationship. I wanted to explore it because I have a hard time trusting women. My girlfriend was absolutely delighted. She said she wanted to try. She had already tried it before and absolutely loved it.<br><br>We thought about it for a bit and decided to do it. I went through a lot with this, but she kept reassuring me. I really wanted to explore something I had never experienced before.<br><br>We agreed that the third person should not be a man. And we decided to look for a woman. We saw a lot of profiles and we finally found her. I'll call her "Lily" for the sake of brevity. Lily was really cute. I was really into her and my girlfriend was too.<br><br>Lily expressed interest in us, we took the plunge and invited her to my place. My girlfriend was absolutely thrilled. We had a great time with Lily. We had never felt so good. We were the three musketeers. I finally felt like I had found my family.<br><br>It's been months since Lily joined us. My girlfriend and Lily are so close that they're like sisters. I don't know what's wrong with me. I know it's wrong to feel this way, but I have this feeling of betrayal. <br><br>A few days ago, I saw Lily and my girlfriend kissing passionately. I was very jealous, but I didn't say anything. It didn't sit right with me and I think they noticed. They were both very cold to me. I asked them if anything was wrong and they said no.<br><br>Yesterday, I saw Lily and my girlfriend having sex. I was in the living room and I thought they were just hanging out in the bedroom, but I walked in on them. They didn't notice me. I was shocked and didn't say anything. When they finished, I hugged them and they didn't seem surprised.<br><br>I can't lie, I was really hurt. I felt betrayed. Lily and my girlfriend were not indifferent to me. They asked if anything was wrong and I said yes. I told them I needed time to myself. They tried to comfort me but I didn't let them. I was so hurt. I was afraid they would leave me.<br><br>Later in the day, I decided to tell them how I felt. I told them that I was complicated and that I was feeling hurt. They were both very calm and just listened. I asked them if they had any physical feelings for each other and they said they were in love with me, but they had discovered mutual feelings of attraction. They told me they were also in a relationship. They wanted me to be part of their relationship. They told me they had tried to include me, but I refused. They said they would take time for themselves.<br><br>I was very shocked. I didn't know what to say. They asked me for time alone. They went on vacation without me for a few days. Lily's mother had a house that was empty. They didn't want to leave me alone and so Lily decided to lend them her mother's house.<br><br>I have the feeling that we are going to break up. I feel so alone. I don't want to lose them. I want them to be happy. I don't know what to do.